RUBY-635 adding 'full_response' option to find_and_modify

This is a pretty trival addon to find and modify. This improvement request came in a long time ago and I guess I just lost track of the ticket, trying to squash it now.

This change adds a :full_response option to the Collection#find_and_modify helper in the same way that the python driver works. This allows users easy access to things like lastErrorObject in the raw response from the server.